dt-bindings: timer: cadence_ttc: Migrate timer-cadence-ttc documentation to YAML

The document was migrated to YAML format and renamed cdns,ttc.yaml.
And updated the example to the latest format.

Signed-off-by: Nobuhiro Iwamatsu <iwamatsu@nigauri.org>
Signed-off-by: Rob Herring <robh@kernel.org>